In recent years, a chucking device is employed in a spindle motor for rotating a disk mounted on a disk driving apparatus about a specified center axis. The chucking device is usually of a type in which the disk is held in place by a plurality of claw members provided in the chucking device. In the chucking device of this type, it is required to use a structure in which the disk is readily attachable but is hardly removed.
A conventional chucking device will be described with reference to FIG. 15. FIG. 15 shows an axially-cut schematic section view of the conventional chucking device wherein a disk KD mounted thereon.
Referring to FIG. 15, the chucking device 1 includes a centering case 2 having a ceiling plate portion 2a and a cylinder portion 2b, a plurality of claw members 3 received in the centering case 2, and a plurality of resilient members 4 for biasing the plurality of claw members 3. A turntable 5 for supporting the disk is arranged on an axial lower side of the chucking device 1 (see, e.g., Japanese Patent Laid-open Publication No. H11-306627).
Since the claw members 3 make contact with the upper edge of a central opening KD1 of the disk KD, the tip end portions of the claw members 3 is in an axially upwardly inclined state. In this state, the radially inward bottom portions of the claw members 3 are brought into contact with the upper surface of the turntable 5. Upon detaching the disk KD, the claw members 3 are caused to move radially inwardly.
The force required in detaching the disk KD (hereinafter referred to as a “detaching force”) is decided by the reaction force acting against the radial inward compression of the resilient members 4 during radial inward movement of the claw members 3 and the frictional force generated by contact between the claw members 3 and the turntable 5. In this connection, if the detaching force is increased by making greater the reaction force acting against the radial inward compression of the resilient members 4, the force required in attaching the disk KD (hereinafter referred to as an “attaching force”) is also increased resultantly, thereby failing to comply with the requirements of the disk driving apparatus. In the meantime, no effort has been made to develop a structure for increasing the frictional force generated by contact between the claw members 3 and the turntable 5, i.e. the detaching force of a disk is increasing without increasing the attaching force thereof.